Method of making drawing dies



April 22, 1941.

L. C. JACOBSON METHOD OF MAKING DRAWING DIES Filed Dec. 16, 1937 l ua"ii /10 ,JZ

II Z 5 INVENTOR Patented Apr. 22,, 1941 METHOD OF MAKING DRAWING DIESLeslie 0. Jacobson, Darien, Conn, assignor to Carboloy Company, Inc.,Detroit, Mich, a corporation of New York Application December 16, 1937,Serial No. 180,080

8 Claims.

The present invention relates to a method of making drawing diesutilizing the class of materials known in the trade as cemented hardmetal carbides, such, for example, as the material described and claimedin the Schroter Patent No. 1,549,615, issued August 11, 1925, consistingof minute particles of extremely hard tungsten carbide cemented togetherwith a small amount of cobalt. Such materials are characterized by verygreat hardness, compressive strength and resistance to abrasion, but donot possess sufflcient tensile strength to withstand the enormous forcesset up in metal drawing operations such as the drawing of wire, rod,tubing and the like.

Drawing dies have heretofore been made by securing nibs of cementedcarbide in casings of materials such as steel or bronze which possesshigh tensile strength and are so designed and made as to reinforce thecemented carbide nib. In prior practice it has been necessary to preparethe casing by accurate machining and the nib by grinding and then tosecure the latter within the former by brazing, or by shrink fitting, orby a forging operation as disclosed, for example, in the patent toMorris Simons 1,952,388, issued March 27, 1934.

A general object of the present invention is the provision of aneffective method for making such dies which may be readily and cheaplypracticed in a minimum amount of time with a minimum amount of labor andmaterial and which results in an eflicient production of reinforced dieswhich are of simple construction and excellent quality, are capable ofwithstanding the enormous forces set up in drawing operations, and havelong lives.

A more specific object of the invention is the provision of an emcientmethod of providing such nibs with metal casing which grip the nibs andplace them under unusually high compression, eliminating the necessityof using supplemental drawing die holders, which method eliminates thenecessity of preliminary annealing of casing material and many machiningoperations and reduces to a minimum Waste of material.

Other objects of the invention will in part be obvious and will in partappear hereinafter.

The invention accordingly comprises the several steps and the relationof one or more of such steps with respectto each of the others thereof,which will be exemplified in the method hereinafter disclosed, and thescope of the invention will be indicated in the claims.

For a fuller understanding of the nature and objects of the inventionreference should be had to the following detailed description taken inconnection with the accompanying drawing, in which:

Fig. 1' is a vertical sectional view of a forging die holder, associatedstructure and a blank or slug of easing material showing a forgingplunger in position prior to a forging operation of the presentinvention;

Fig. 2 is a sectional view similar to Fig. 1 showing a nib-receivingrecess being forged into the casing blank or slug;

Fig. 3 is a similar sectional view showing the upper portion of thecasing blank or slug being forged over the upper end of a nib seated inthe casing recess; and

Fig. 4' is a vertical sectional view of a completed reinforced die.

By the present invention a recess adapted to receive a cemented hardmetal carbide nib is forged into a slug or flat blank of tool steel orother suitable material of high tensile strength to form a cup-shapedcasing and a nib is then placed into the cup-shaped casing and securedtherein by forging, producing a drawing die of superior strength andeliminating to a large extent the machining and grinding operations andwaste of high priced material which is characteristic of the practicesheretofore followed.

The application of the present invention will be described withparticular reference to the production of a wire drawing die having anib of cemented tungsten carbide provided with a circular metal drawingpassageway and surrounded by a casing of tool steel containing about.80% to 1.05% carbon, about 20% to .45% vanadium and, if desired, up toabout .5% chromium, though it is to be understood that the invention isapplicable to the production of drawing dies of other designs, with nibsof other materials of the same class, and with casings of othermaterials having the necessary properties of high elastic strength andthermal expansion.

Cylindrical bar stock of the selected tool steel in unannealed conditionis cut by means of an abrasive wheel cutting machine into sections ofpredetermined length, with substantially flat end faces. Each of thesesections constitutes a casing slug or blank [0. Without furthermanipulation of any kind, each slug I0 is heated to a suitable forgingtemperature between about 1850 F. and 2000 F. to make it plastic. It isthen transferred quickly to a cup-shaped forging die I l, formed of hotforging steel such as chromiumtungsten steel or other suitable material,in a press of the type adapted to deliver percussive compression or arelatively slow hammer blow effect, such as a percussion, hydraulic orcompression screw press. The forging die ll preferably has the walls ofthe socket l2 therein tapered slightly and is provided with an ejectionpassage B in the bottom thereof to permit ready removal of a completeddie assembly. A bottom plate I4, preferably formed of similar metallicmaterialIi's seated in the bottom of the socket l2.

A press plunger I5 is centered on top of the hot sing I and the press isoperated to drive or force the plunger into the slug Ill to the desireddepth displacing slug material to form a recess It as shown in Fig. 2.The plunger is driven or forced into the hot slug I0 preferably to anextent so that a portion ll of the top of the resultant cup-shapedcasing projects above the upper end of a nib when placed in the recess.

The casing may then be permitted to cool, placed in stock andsubsequently reheated to forging temperature and a nib I8 seated in therecess it after reheating, or a nib may be placed into the recessimmediately after formation of the latter before the casing has cooledbelow a forging temperature, and another press plunger I!) having acentrally located stud on the end thereof may be operated to cause theportion H of easing material to flow over the outer portion of the upperend of the nib l8 as shown in Fig. 3. During this second forgingoperation which is similar to that described in the identified Simonspatent the stud 20 limits the inward flow of the casing material. Thenib is thus "positioned in the recess with the walls thereof snuglyengaging the nib when the casing is hot either by the seating of the nibwhen the casing is reheated or by the placement of the nib immediatelyafter formation of the casing before it has cooled.

The encased nib is then ejected from the forging die H and allowed tocool to and is heat treated at about 800 F. to permit contraction of thecasing so that it will place the nib under great compression. Thereafterthe casing is tempered at about 900 F. to 1250 F., preferably about 1150F., to-develop the proper properties in the casing steel. After thetempering is complete, the casing material at the center of the bottomof the die is removed by a simple trepanning tool to form an opening 2I. All that is necessary to finish the tool is to make and/or finish awiredrawing hole 22 in the nib l8, to machine the outer surface 23 ofthe casing to insure concentricity with the hole 22 and, if desired,machine out opening 24 in the casing communicating with the wire-drawinghole.

If desired, although not necessary, the nib may have its surfaces groundand/or sand blasted to remove surface defects or adhesions prior tobeing placed in the casing and may be preheated. The nib may be a blanknib or a cored nib, i. e. a nib provided with a wire-drawing hole. If ablank nib is used, it is preferably provided with a center 25 prior tobeing positioned in the casing to permit ready machining of thecircumferential face of the casing concentric with the axis of the niband to facilitate opening up the bottom of the casing.

7 The plunger l5 may be centered on the hot slug ill in any suitablemanner. This may be done by placing a centering ring within the socket[2 on the top of the hot slug In with the outer surface of the ringsnugly fitting within the socket l2. and a centered hole in thereceiving and guiding the plunger l5.

Obviously such centering ring will not be necessary if provision is madefor accurate placement of the forging die ll beneath a plunger fittedinto the head of the press with the axis of the casin slug l0 coincidingwith that of the plunger. If the plunger I5 is a punch fitted into thehead of the press it will accomplish the first forging operation, thatof forming the recess I8, as shown in Fig. 2, when the press head ismoved on the downstroke. On the upstroke the punch may be retracted fromthe recess l8 into which a die nib can then be placed. A second plungerI9 which may be fitted into the head of the press can then be moved intoposition and the second forging operation shown in Fig. 3 can beaccomplished when the press head is moved on the succeeding downstroke.Both forging operations can thus be easily and rapidly performed beforethe casing material has cooled below a forging temperature. Thestructure of the press may be such that the two plungers l5 and I9 maybe shifted automatically so that they are successively centered over thecasing being forged.

Materials other than tool steel may be used for the casing. Suchmaterials should have high tensile strength and higher coefiicient ofthermal expansion than the nib material. Various types of bronze, suchas aluminum bronze known as Avialite, satisfy these requirements. Asuitable forging temperature for bronze is about 1500 F.

The casing slug may be heated to the forging temperature in a period ofminutes. The slug ID at the forging temperature should fit easily intothe socket I 2 of the forging die II which preferably is cold when theheated slug is placed therein. Consequent chilling of the surface of theslug eliminates any tendency for it to weld to the socket face of theforging die.

By the present invention the manufacture of cemented carbide drawingdies is greatly simplifled and the expense materially reduced. Forexample, the steel bar stock can be used in the unannealed condition,thus eliminating the expense of annealing which has heretofore beennecessary. Preliminary machining of the casing material is entirelyeliminated. Waste of steel is eliminated with the exception of a verysmall amount which is trimmed from the casing after the forgingoperation is completed. The amount of final grinding of the casing toinsure its concentricity with the hole in the nib is reduced to aminimum.

In addition to the elimination of machining and grinding operationsheretofore necessary and the elimination of waste, the present inventionmakes possible the production of drawing dies of superior strength anddecreased liability to breakage in service.

In the claims the use of the terms "hard metallic nib and slug of casingmaterial are used respectively to identify hard metallic material havinglow tensile strength, great hardness, high melting point and lowcoeflicient of thermal expansion, such as a cemented hard metal carbide;and metallic casing material which is deformable and has high tensilestrength and a higher ring 0 coefllcient of thermal expansion than thenib material, thus high shrinkage characteristics.

-It will thus be seen that the objects set forth above are attained bythe present invention in an eflicient manner. Since certain changes maybe made in carrying out the above method without departing from thescope of the invention, it is intended that all matter contained in theabove description shall be interpreted as illustrative and not in alimiting sense.

It is also to be understood that the following claims are intended tocover all of the generic and specific features of the invention hereindescribed, and all statements of the scope of the invention which, as amatter of language, might be said to fall therebetween.

Having described my invention, what I claim as new and desire to secureby Letters Patent, is:

1. The method of making a drawing die, comprising heating a slug ofcasing material to a forging temperature, hot-forging a recess thereinto form a cup-shaped casing while limiting lateral expansion of thecasing material, positioning a hard metallic nib in said recess andcooling the cup-shaped casing about said nib to thereby place the nibunder high compression.

2. The method of making a drawing die, comprising heating a slug ofeasing material to a forging temperature, hot-forging a recess thereinto form a cup-shaped casing while limiting lateral expansion thereof,positioning a hard metallic nib in the recess with the walls thereofsnugly engaging the nib when the casing is hot,

hot-forging a portion of said casing over the upper end of said nib andheat treating the resulting assembly,

3. The method of making a drawing die, comprising heating a slug ofcasing material to a forging temperature, hot-forging a recess thereinto form a cup-shaped casing, positioning a hard metallic nib in saidrecess so that a portion of said casing projects above the upper end ofsaid nib, hot-forging the portion of said casing pro- Jecting above theupper end of said nib over the upper end of said nib, and limitinglateral expansion of the casing material during forging.

4. The method of making a drawing die, comprising heating a slug ofeasing material to a forging temperature, hot-forging a recess thereinwhile limiting lateral expansion to form a cupshaped casing, seating ahard metallic nib in the recess before the casing has cooled below aforging temperature, and hot-forging a portion of said casing over theupper end of said nib.

5. The method of making a drawing die, comprising heating a slug ofeasing material to a forging temperature, hot-forging a recess thereinwhile limiting lateral expansion to form a cup shaped casing, seating ahard metallic nib in the recess with the casing at a forgingtemperature, hot-forging over the upper end of said nib a portion ofsaid casing projecting thereabove, and

heat treating the resulting assembly.

6. The method of making a drawing die, comprising heating a slug ofsteel of high compressive strength to a forging temperature, hot-forginga recess therein while limiting lateral expansion to form a cup-shapedcasing, positioning a hard metal carbide nib in therecess with thecasing at a forging temperature,'hot-forging a portion of said casingover the upper end of said nib and cooling the steel casing to cause itto place said nib under high compression.

7. The method of making a drawing die which comprises heating a slug ofeasing material to a forging temperature, placing said heated slug in aforging die, hot-forging a recess in said slug to form a cup-shapedcasing that is wholly within said forging die,'positioning a die nib insaid recess so that the cup-shaped casing extends above said nib, andhot-forging a portion of said casing over the upper end of said nib.

8. The method of making a drawing die which comprises heating a slug ofeasing material to a forging temperature, placing said heated slug in aforging die, hot-forging a recess in said slug to form a cup-shapedcasing, thereafter positioning a cored die nib in said recess so thatthe cup-shaped casing extends above said nib, hot-forging a portion ofsaid casing over the upper end of said nib and heat treating theresulting assembly.

LESLIE C. JACOBSON.

